Good Friday is observed in what is known as Holy Week in the Christian tradition. Historically, Holy Week begins with Palm Sunday, the day when Jesus entered Jerusalem among a crowd of well-wishers waving palm branches at Him as He rode by. The Bible reveals a number of events during the succeeding days, including the Passover meal (which became known as the Last Supper) observed by Jesus and His disciples on Thursday evening, followed by His arrest and trials and beatings, and eventually leading to His crucifixion on Friday.
Good Friday is good, in the Christian sense, because Jesus, the Bible declares, died on the cross for the sins of the whole world. His death on Friday was followed by His burial and then a miraculous resurrection on Sunday morning, the day traditionally observed as Easter.
History.com summarizes this celebration as follows:
Easter is a Christian holiday that celebrates the belief in the resurrection of Jesus Christ. In the New Testament of the Bible, the event is said to have occurred three days after Jesus was crucified by the Romans and died in roughly A.D. 30. The holiday concludes the “Passion of Christ,” a series of events and holidays that begins with Lent—a 40-day period of fasting, prayer and sacrifice—and ends with Holy Week, which includes Holy Thursday (the celebration of Jesus’ Last Supper with his 12 Apostles, also known as “Maundy Thursday”), Good Friday (on which Jesus’ crucifixion is observed) and Easter Sunday.
There have been many variations on the type and timing of the events of Passion Week within the Christian church, as well as in pagan societies through the ages, but all of these traditions are focused on the events of Good Friday and the resurrection of Jesus three days later.
For more details about Good Friday, check out the following links:
What is Good Friday / Holy Friday? | GotQuestions.org
Easter – Dates, Easter Eggs & Easter Bunny | History.com)